1. Field of the Invention
The present invention relates to the crushing and grinding of materials. More specifically, this invention is directed to ferrous alloys suitable for use in crushing and grinding devices, such as balls and rods, and for use in attrition members, such as the lining plates of crushing and grinding mills, crushing jaws and the like, which are subjected to abrasion and repeated shocks. Accordingly, the general objects of the present invention are to provide novel and improved methods and materials of such character.
2. Description of the Prior Art
While not limited thereto in their utility, alloys prepared in accordance with the present invention are particularly well suited for use in the crushing or grinding of materials in a moist medium, including liquid moist mediums comprising hot and corrosive gases, and also in processes and apparatus which simultaneously crush and dry materials. In the industries concerned with wet grinding and crushing techniques attempts have been made to use special types of cast iron and steels as grinding elements or in crushing devices; the excellent wear resistance properties of these materials having been proven in dry grinding operations. For example, cast iron containing 4% nickel and 1.5% chromium in the as-cast condition, with or without tempering, has been proposed for use in dry grinding. Similarly, it has been proposed to use hardened 12% chromium cast iron, cast iron containing 15% chromium and 3% molybdenum in the as-cast or hardened condition, cast iron containing 26% chromium in the as-cast or hardened condition and 12% manganese austenitic steels for dry grinding. These prior art alloys have not proved economical for a number of reasons and, accordingly, at present the practice in the art is to employ the least expensive available materials for crushing and grinding operations. Such inexpensive materials include ordinary steel, low chromium alloyed perlitic white iron and, on occasion, ore, blocks of silica, or pebbles or bolders from a local river or sea shore have been used. In short, it is presently considered preferable to re-equip grinding mills regularly with these inexpensive materials or devices formed thereof in view of the lack of availability of materials having high resistance to wear which are competitively priced.
It is known that when grinding in a moist medium wear depends primarily on two factors; these factors being abrasion and corrosion. In order to resist abrasion, steels or cast iron having a high content of carbon and carbides, preferably in a hardened condition, must be used. In order to resist corrosion, it is necessary to employ, in the surfaces which will actually accomplish the grinding, alloys having a high chromium content. Although the necessity of providing abrasion and corrosion resistance and the materials which offer these characteristics are well known, alloys with a high carbon and a high chromium content have not previously been employed in grinding apparatus because it has not previously been possible to combine a suitable choice of composition of alloy with a suitable heat treatment procedure in such a manner as to economically obtain materials having the desired abrasion and corrosion resistance characteristics.